CN1841819B - battery cathode material - Google Patents

Abstract

Provided is a positive electrode material for batteries, which has good electrical conductivity and is cheaper to prepare than AgNiO ₂ . The positive electrode material of the battery is a conductive compound with a general formula of Ag _x Ni _y O ₂ (where X/Y is less than 1 but not less than 0.25). The conductive compound is composed of crystals having the same main X-ray diffraction peaks as AgNiO ₂ (where X=Y=1), and no characteristic peaks of Ag ₂ O or AgO. This conductive compound can be used as an additive to impart conductivity to silver oxide (Ag ₂ O) in positive electrode materials.

Description

battery cathode material

technical field

The invention relates to a material for battery positive poles.

Background technique

Small silver oxide alkaline batteries (often called button cells) are widely used. In a silver oxide battery, the positive electrode material is silver oxide, the negative electrode material is zinc powder, and the electrolyte is an alkaline solution, such as an aqueous solution of KOH or NaOH. Silver oxide has a high service capacity (discharge capacity), but due to its high resistance, which is close to an insulator, it is often mixed with a conductive material such as graphite to make the positive electrode material conductive.

References 1-3 disclose the use of silver-nickel composite oxide _AgNiO2 as a battery cathode material. For example, reference 1 ₍ JP S57-849A) describes the flat discharge voltage curve of a battery with a positive electrode formed of AgNiO ₂ , which was synthesized by reacting equimolarly (molar ratio 1:1) with silver nitrate and nickel nitrate. Reference 2 (JP H10-188975A) describes a manufacturing method for optimizing the reaction of synthesizing AgNiO ₂ , and a battery using the AgNiO ₂ as a positive electrode material has stable discharge characteristics. Reference 3 (US 2002/0127469 A1 ) describes a button cell containing a mixture of _AgNiO2 with silver oxide or manganese dioxide in the electrode container.

purpose of invention

Batteries with positive electrodes composed of _AgNiO2 as documented in ref. have the potential for high capacity and stable discharge performance. However, these techniques have not been implemented in practice. Current silver oxide batteries generally use silver oxide as the positive electrode material, in which an appropriate amount of graphite is mixed for conductivity.

One of the reasons for this is that although _AgNiO2 has a lower silver content than silver oxide, its production process is complicated and the unit cost of the oxidizing agent is quite high. Therefore, when AgNiO ₂ is produced with equipment of the same scale as silver oxide, it is not necessarily possible to obtain an inexpensive material. Therefore, users want to find battery cathode materials that are cheaper than _AgNiO2 and have good conductivity.

The object of the present invention is to provide anode materials for batteries, which are cheaper to prepare than _AgNiO2 and have good electrical conductivity.

Contents of the invention

Based on the results of a large number of experiments and researches, the inventors found that the Ag _x Ni _y O ₂ -based composite oxide has a lower silver content than AgNiO ₂ , but has better conductivity, and its active material properties make it suitable as a positive electrode material. When this composite oxide is mixed with silver oxide and formed into pellets or spheres, it has a low silver content but exhibits good electrical conductivity, which also makes it suitable as a positive electrode material.

That is to say, the present invention provides a battery positive electrode material, which contains a conductive compound with the general formula Ag _x Ni _y O ₂ (where X/Y is less than 1 but not less than 0.25). This battery cathode material is a conductive compound composed of crystals, which have the same X-ray diffraction main peaks as AgNiO ₂ (where X=Y=1), but there are no characteristic peaks of Ag ₂ O and AgO crystals, nor There are characteristic peaks of Ni(OH) ₂ and NiOOH crystals. Mixing this conductive compound with silver oxide ( _Ag2O ) yields a cathode material with excellent electrical conductivity and discharge performance. The conductive compound can be prepared by the following method: Ag salt and Ni salt are reacted in water to generate a precipitate of a compound having the general formula Ag _x Ni _y O ₂ (wherein X/Y is less than 1, but not less than 0.25), and from the liquid The precipitate was isolated, washed and then dried in a _CO2 -free atmosphere.

This battery cathode material of the present invention is cheaper than AgNiO ₂ , has good electrical conductivity and can be used as an active material. Therefore, in addition to being used as a positive electrode material alone, it can also be mixed with silver oxide to form a battery positive electrode material with low resistance, excellent discharge performance, and low cost because its silver content is lower than that of silver oxide.

Description of drawings

Figure 1 is an X-ray diffraction pattern of Ag-excess Ni oxide according to the present invention compared to _AgNiO2 .

Fig. 2 is the electrical resistivity of battery anode materials containing Ag-excess Ni oxide mixed with silver oxide of the present invention.

Detailed ways

As described above, the present inventors provided a compound having the same crystal structure and discharge performance as AgNiO ₂ even though its nickel content is higher than that of AgNiO ₂ . Although the Ag/Ni molar ratio of this compound is less than 1 and therefore smaller than the _{corresponding} molar ratio of _AgNiO2 , _its crystal structure is identical to that of _AgNiO2 and is thus represented by the general formula _AgxNiyO2 (X/Y<1). Preferably, X/Y is 0.92 or less, but not less than 0.25.

This compound may be called an Ag-excess Ni delafossite-type oxide, hereinafter simply referred to as "Ag-excess Ni oxide". Similar to AgCoO ₂ , etc., AgNiO ₂ can also be considered as a delafossite-type oxide and is represented by ABO ₂ , where A is a monovalent metal and B is a trivalent metal. The crystal structure of delafossite-type oxides contains alternating filling layers of AOBO-, so despite being an oxide, it is also conductive. In the Ag-excess Ni oxides of the present invention, since Ag and Ni are not equimolar, the excess Ni may appear to be a departure from the originally defined delafossite-type oxide. The present inventors have clarified that they have the same crystal structure and show good conductivity. In Japanese Patent Application No. 2004-375474, the present inventors disclosed a battery positive electrode material having the same crystal structure as AgNiO ₂ and containing excess Ag.

FIG. 1 shows the comparative X-ray diffraction diagrams of the Ag-excess Ni oxides of Examples 3 and 4a (described later) of the present invention and AgNiO ₂ of Comparative Example 3. As shown in Figure 1, the Ag/Ni molar ratio of Ag-excess Ni oxide in Example 3 is 0.6/1.40, that is, X/Y=0.43, and the Ag/Ni molar ratio of Ag-excess Ni oxide in Example 4a is 0.4/1.60, that is, X/Y=0.25, and their main diffraction peaks overlap with those of the AgNiO ₂ compound in Comparative Example 3, and other peaks also basically overlap. In the Ag-excess Ni oxide of the present invention, Ni may exist in the form of solid solution in the Ag layer of the AOBO-alternating filling layer of the delafossite-type oxide (in the compound of the present invention, it is Ag-O-Ni -O layer). However, the Ag ⁺¹ ion radius is about 1.7 times that of Ni ⁺³ ion radius, and the solid solution range of Ni is limited by itself. Therefore, when Comparative Example 6 in Fig. 1 contains a large amount of excess Ni, other peaks near 2θ=19° and 43° appear, indicating that other phases coexist.

The Ag-Ni excess oxide of the present invention can be used as positive electrode material alone. However, by replacing part of the silver oxide used as the positive electrode material in silver oxide batteries, a high-performance positive electrode material with good conductivity can be obtained, even if the material is not mixed with graphite or the like. The conductivity of silver oxide can be improved by adding as little as a few weight percent (wt%) of Ag-excess Ni oxide. Therefore, its addition amount is set to be 2 wt% or more, preferably 3 wt% or more, more preferably 5 wt% or more.

In the following examples of the present invention, the conductive compound Ag _0.8 Ni _1.2 O ₂ is mixed with silver oxide to form pellets, and the relationship between the mixing ratio and the resistivity of the pellets is plotted and shown in FIG. 2 . The symbol ■ represents the embodiment of the present invention, and the figure shows that when the mixing ratio increases to 25%, the resistivity drops rapidly. In Fig. 2, the symbol ♦ represents the same relationship of the comparative example in which the conductive compound AgNiO ₂ (using AgNiO ₂ in Comparative Example 3) and silver oxide is mixed, as can be seen from the figure, although the silver content is lower than that in the comparative example , but it is not bad at improving conductivity when mixed with silver oxide. Symbol ▲ represents the situation of Comparative Example 6, wherein Comparative Example 6 is used as a reference example material, which contains other phases shown in Fig. 1 and is mixed with silver oxide. Here, even when it is mixed with silver oxide, the resistivity decreases slowly, so its effect of improving conductivity is poor.

The Ag-excess Ni oxide conductive compound of the present invention can produce silver-nickel oxide precipitation containing excess nickel by reacting Ag salt and Ni salt in water, and adding oxidizing agent and adopting sufficient ripening prevents generation such as silver oxide and hydroxide The secondary product of nickel, and then form a single-phase Ag-excess Ni oxide.

Through experiments, the inventors found that when Ag salt and Ni salt reacted in water to form a silver-nickel oxide precipitate containing excess nickel and dried the oxide in the common atmosphere, the particle color was brown, and did not reach the level based on its silver content. content should reach the discharge capacity. The reason is that _CO2 in the atmosphere is easily adsorbed due to the high specific surface area of the silver-nickel oxide containing excess nickel. When the oxide reacts with CO2 _, silver carbonate, which is readily soluble in alkali, is formed. Therefore, it is considered that when this material is used as a cathode material, it dissolves in an alkaline electrolyte, causing short circuit and self-discharge that degrades the separator. The reaction to produce silver carbonate proceeds more easily in the drying step than in the wet reaction, so it is considered that the reaction of _CO2 and silver is promoted by thermal energy by the trace amount of water passing through the particle surface in the drying step. Therefore, it is desirable to avoid contact with _CO2 in the atmosphere of the drying process as much as possible. In practice, drying may be carried out under nitrogen, argon or other such inert gases, decarbonized air or vacuum. That is, after synthesizing a single-phase Ag-excess Ni oxide with the above method, the battery cathode material with good discharge performance was obtained by separating the precipitate from the liquid, washing and drying in a _CO2 -free atmosphere.

In the present invention, the Ag-excess Ni oxide can also be obtained by reacting the mineral acid salt of Ag and the mineral acid salt of Ni in the oxidizing alkaline aqueous solution, and the steps are as follows:

(1) The inorganic acid salt of Ag and the inorganic acid salt of Ni are reacted in an aqueous solution containing an alkali metal hydroxide to obtain a neutralized precipitate.

(2) Adding an oxidizing agent to the solution or the obtained precipitate suspension before or during the above-mentioned neutralization reaction for oxidation treatment to increase the valence of the metal ion. Preferably, the oxidizing agent is added several times before the neutralization reaction and after the neutralization reaction.

(3) Separate the precipitate from the liquid after the oxidation treatment, wash and dry the precipitate in a _CO2 -free atmosphere, and pulverize the dried cake into powder.

NaOH or KOH can be used as alkali metal hydroxide for neutralization reaction. Although nitrates, sulfates, hydrochlorides, phosphates, etc. of respective metals can be used as the salts of Ag and Ni, their nitrates or sulfates are preferably used. Typically, the nitrates of the respective metals can be used. As with AgNO ₃ , Ni(NO ₃ ) ₂ may be used with a desired molar number.

Higher alkalinity favors the neutralization reaction. For example, when Ag+Ni+M, in terms of molar ratio, it is more conducive to the reaction under about 5 times of alkaline conditions. Both the neutralization and the oxidation treatment can be carried out at a reaction temperature of room temperature to 100°C, preferably at a temperature of 30 to 50°C. It is necessary for the stirring to be strong enough to allow the neutralization and oxidation reactions to proceed uniformly. Even after the reaction, stirring should be continued at the desired temperature to ensure ripening.

The Ag/Ni ratio of the final compound and correspondingly the Ag/Ni atomic ratio in the particles can be adjusted from 0.25 to less than 1 by adjusting the molar ratio of silver nitrate and nickel used in the reaction.

Oxidative treatment involves the use of oxidizing agents to increase the valency of metal ions. The oxidizing agent can be added at the beginning of, during the neutralization reaction or into the precipitated suspension. Therefore, neutralization and oxidation treatment can be carried out separately or simultaneously. It is preferred that the oxidizing agent is added in several batches before, during and after the neutralization reaction. Stirring is required during the oxidation treatment, and the temperature should not exceed 100°C, because too high a temperature will promote the decomposition of the oxidizing agent. Substances that can be used as oxidizing agents include, for example, KMnO ₄ , NaOCl, H ₂ O ₂ , K ₂ S ₂ O ₈ , Na ₂ S 2 O ₈ and ozone, but K _{2 S 2} O ₈ , Na ₂ S ₂ O ₈ are preferably used or ozone, because impurities in the Ag-excess Ni oxide powder can be reduced by using an oxidizing agent. The amount of oxidizing agent must be sufficient to change the valency. The above effects can be obtained by adding an oxidizing agent in an amount corresponding to the change in valence at least, preferably about twice the amount.

Example

Before introducing the examples, the method for checking the properties of the powders obtained in each example is explained.

Particle size: The measurement of particle size is the Helos laser diffraction analyzer manufactured by Sympatec GmbH, which disperses the particles in the drying system with high-pressure gas, and uses laser diffraction to measure the particle size. Compared to wet measurements, which are easily affected by the affinity between the sample and the solvent, this dry measurement ensures that the particle size is measured without this influence, so that the measured values of the materials are very reproducible . The dispersing pressure can be adjusted as required, and a dispersing pressure of 4.00 bar is used in this embodiment.

X-ray diffraction: An X-ray diffractometer manufactured by Rigaku Corporation was used. In the measurement, a CuKα X-ray source was used, and the measurement was performed at an X-ray voltage of 50 kV and a current of 100 mA.

Specific surface area: The BET method was adopted, and the above measurement was performed using a Quantachrome Jr surface analyzer manufactured by Quantachrome Corporation.

Chemical analysis: Dissolve the sample in nitric acid for chemical analysis by titration.

_CO2 analysis: JIS R9101 method is adopted.

Battery evaluation: The service capacity of the sample powder was measured by a three-electrode battery. The measurement was carried out using a composite sample prepared as follows: about 100 mg of a mixture consisting of 95% sample powder and 5% PTFE was molded into a cylinder with a base plate area of 1.77 cm ² , and then the molded cylinder was bonded by pressure. bonded to a stainless steel mesh current collector to form a composite sample. Metal zinc sheet was used as reference electrode and negative electrode; 50mL40% KOH solution was used as electrolyte. The discharge capacity was measured when the voltage reached 1.2V.

Resistivity: Through the pressure of 3t/ ^cm2 , each powder sample becomes a cylindrical pellet with a cross-sectional area of ^1cm2 , and the area of the copper electrode sheet bonded to the top and bottom of each pellet is larger than the cross-sectional area of the pellet. The pellets sandwiched between the electrode sheets are placed flat on a stainless steel table, and a stainless steel weight of 130kgf load is applied on it. In this state, each electrode lead was connected to a resistivity tester, and the resistance between the electrodes (resistance of the pellet) was measured. Measure the resistance value of the equipment without pellets in advance to correct the measured value of pellet resistance.

Molding density: A metal mold formed with a vertical through hole with a cross-sectional area of 1 cm ² is made, a base having the same diameter as the hole is put into the hole, and 1 g of sample powder is put on the base. Insert a punch with the same diameter as the hole and apply a pressure of 3t for 3 minutes to compress the powder. The molding density can be calculated from the weight and thickness of the molded product after molding.

Comparative example 1

The silver content, discharge capacity, molding density and resistivity of powdered silver oxide (Ag ₂ O produced by Dowa Mining Co., Ltd., with an average particle size of 15 μm) used as a commercial positive electrode were measured, and the results are shown in Table 1. This silver oxide has a purity of 99.9 percent or better, calculated on silver content. Its discharge capacity is 220mAh/g, close to the theoretical capacity of silver oxide.

Comparative example 2

The silver content, discharge capacity, molding density and resistivity of granular silver oxide (produced by Dowa Mining Co., Ltd., with an average particle size of 105 μm) used as a commercial positive electrode were measured, and the results are shown in Table 1. Its discharge capacity and resistivity were the same as those of Comparative Example 1.

Comparative example 3

This comparative example involves AgNiO ₂ (X/Y=1.0/1.0).

Put 0.5 liter of pure water, 3.0 mol of NaOH and 0.5 mol of sodium persulfate into a 1 liter beaker, and adjust the temperature of the solution to 30°C. 1 liter of an aqueous silver nitrate solution containing 0.25 mol of silver equivalent was added to the solution over 30 minutes, and the solution was kept at 30°C for 1 hour.

1 liter of nickel nitrate aqueous solution containing 0.25 mol of nickel was added to the solution in 30 minutes, and the solution was kept at 30° C. for 4 hours to complete the reaction. The reactant slurry was filtered to obtain a black filter cake. The filter cake was thoroughly washed with pure water and dried in vacuum at 100°C for 12 hours. Crush the dried cake with a pestle. When the resulting black powder was confirmed by X-ray diffraction, it was confirmed to be AgNiO ₂ . The X-ray diffraction pattern of the powder is shown in Figure 1. The evaluation test results of the powder are shown in Table 1.

Example 1a

This example relates to _AgxNiyO2 (X/ _{Y =} 0.96/1.04).

Put 0.5 liter of pure water, 3.0 mol of NaOH and 0.25 mol of sodium persulfate into a 1 liter beaker, and adjust the temperature of the solution to 30°C. 1 liter of an aqueous silver nitrate solution containing 0.24 mol of silver equivalent was added to the solution over 30 minutes, and the solution was kept at 30°C for 2 hours.

1 liter of an aqueous nickel nitrate solution containing 0.26 mol of nickel equivalent was added to the solution over 30 minutes, and the solution was kept at 30°C for 2 hours. Then, 0.25 mol of sodium persulfate was further added to the solution, and the solution was maintained at a temperature of 30° C. for 12 hours to terminate the reaction. The reactant slurry was filtered to obtain a black filter cake. The filter cake was washed with pure water and dried in vacuum at 100°C for 12 hours. Crush the dried cake with a pestle. When the obtained black powder was confirmed by X-ray diffraction, it was found to be similar to the diffraction peak of _AgNiO2 in Comparative Example 3. The evaluation test results of the powder are shown in Table 1.

Example 1b

The same procedure as in Example 1a was repeated except that carbon-free air was used instead of vacuum in the process of drying the filter cake after washing. Carbon-free air is obtained by passing air through molecular sieves. The evaluation test results of the powder are shown in Table 1. The obtained test values for _CO2 analysis and discharge capacity were the same as for the powder of Example 1a.

Comparative example 4

The same procedure as in Example 1a was repeated except that air was used instead of vacuum in the process of drying the filter cake after washing. The evaluation test results of the powder are shown in Table 1. Compared with Examples 1a and 1b, the powder has a higher _CO2 content and a lower discharge capacity.

Example 2

_{This example relates to AgxNiyO2 (} X/Y ₌ 0.80/1.20). It was the same as Example 1a except that silver nitrate corresponding to 0.2 mol of silver and nickel nitrate corresponding to 0.3 mol of nickel were used. When the resulting black powder was confirmed by X-ray diffraction, its diffraction peaks were found to be similar to those of _AgNiO2 in Comparative Example 3. The evaluation test results of the powder are shown in Table 1.

Example 3

_{This example relates to AgxNiyO2 (} X/Y ₌ 0.60/1.40). It was the same as Example 1a except that silver nitrate corresponding to 0.15 mol of silver and nickel nitrate corresponding to 0.35 mol of nickel were used. When the resulting black powder was confirmed by X-ray diffraction, as shown in Fig. 1, its diffraction peaks were found to be similar to those of AgNiO in Comparative Example ₃ , and no peaks of silver oxide, nickel hydroxide or the like were observed. The evaluation test results of the powder are shown in Table 1.

Example 4a

_{This example relates to AgxNiyO2 (} X/Y ₌ 0.40/1.60). It was the same as Example 1a except that silver nitrate corresponding to 0.10 mol of silver and nickel nitrate corresponding to 0.40 mol of nickel were used. As shown in FIG. 1 , the diffraction peaks similar to those of AgNiO ₂ in Comparative Example 3 were observed, and no peaks of silver oxide, nickel hydroxide, or the like were observed. The evaluation test results of the powder are shown in Table 1.

Example 4b

The same procedure as in Example 4a was repeated except that carbon-free air was used instead of vacuum when drying the filter cake. Carbon-free air is obtained by passing air through molecular sieves. The evaluation test results of the powder are shown in Table 1. Its _CO2 analysis and test value of discharge capacity are about the same as those of Example 4a.

Comparative Example 5

The same process as in Example 4a was repeated except that air was used instead of carbon-free air when drying the filter cake. The normal air used has not been decarbonized etc. The evaluation test results of the powder are shown in Table 1. Compared with Examples 4a and 1b, the _CO2 content of this powder is much higher, while the discharge capacity is much lower.

Comparative example 6

This comparative example involves Ag _x Ni _y O ₂ (X/Y=0.20/1.80). It was the same as Example 1a except that silver nitrate corresponding to 0.05 mol of silver and nickel nitrate corresponding to 0.45 mol of nickel were used. When the resulting black powder was determined by X-ray diffraction, as shown in Figure 1, peaks similar to those of _AgNiO2 could be observed, but there were also peaks different from those of AgNiO near 2θ=43° and 2θ=19°. ₂ peaks of other substances. The evaluation test results of this powder are shown in Table 1. Compared with the material of the embodiment of the present invention, its discharge capacity is lower and its resistivity is higher.

The results shown in Table 1 reveal the following:

(1) According to the comparison of Examples 1-4 and Comparative Example 3, although the Ag-excess Ni oxide of the present invention contains more excess Ni than AgNiO ₂ , its crystal structure is the same as that of AgNiO ₂ . Despite its low silver content, it is used as a low resistivity material with good electrical conductivity.

(2) Furthermore, the composition of the material, which has a low silver content and is used as an active material, shows a discharge capacity corresponding to the silver content.

(3) However, when the Ni content is too large, as in the case of Comparative Example 6, a phase other than AgNiO ₂ appears, lowering the conductivity.

Example 5

In this example, the conductive compound composed of excess Ag-Ni oxide was mixed with silver oxide to make pellets, which were used as the positive electrode material of the battery, and the resistivity of the material was tested.

As a "comparative example", the AgNiO ₂ of Comparative Example 3 and the silver oxide of Comparative Example 1 were mixed in different ratios to make pellets, and the resistivity of the pellets was tested. See Table 2 for the test results and the silver content (wt %) of the pellets.

For the "embodiment" of the present invention, use Ag _0.8 Ni _1.20 O in embodiment ₂ and the silver oxide in comparative example 1 to make pellets after mixing in different ratios, and test the resistivity of various situations, the results are shown in Table 2 .

For "Reference Example", the powder in Comparative Example 6 and the silver oxide in Comparative Example 1 were mixed in different ratios to make pellets, and the resistivity of various situations was tested. The results are shown in Table 2, and Fig. 2 is based on The resistivity numerical graph drawn from the data in Table 2.

Table 2

As can be seen from Table 2 and FIG. 2, the pellets formed by mixing the Ag-excess Ni oxide and silver oxide of the present invention have the same conductivity-imparting effect as _AgNiO2 , although their silver content is lower than that _{of AgNiO2} . Since the powder of Comparative Example 6 contained other phases than the conductive compound, it did not have the excellent conductivity-imparting effect brought about by the effect of the Examples of the present invention.

Claims (3)

1. a cell positive material comprises by general formula Ag _xNi _yO ₂The conductive compound of expression, wherein X/Y is no more than 0.92, but is not less than 0.25, and wherein this compound is the superfluous N i of an Ag-oxide, its X-ray diffraction main peak and the AgNiO of X=Y=1 wherein ₂Identical, and do not have Ag in its crystal that comprises ₂O and AgO X-ray diffraction in crystals characteristic peak, and do not have Ni (OH) in its crystal that comprises ₂With NiOOH X-ray diffraction in crystals characteristic peak.

2. a cell positive material comprises the described cell positive material of the claim 1 of mixing with silver oxide.

3. make the method for cell positive material according to claim 1 for one kind, described method comprises reacts Ag salt and Ni salt in the presence of oxidant in water, be settled out with general formula Ag _xNi _yO ₂The compound of expression, wherein X/Y is not more than 0.92 but be not less than 0.25; Precipitation separation from liquid washs this precipitation and is not containing CO ₂Atmosphere in dry should precipitation.